1. Field of the Invention
The present invention generally relates to robotics and, more particularly, to a robot hand that includes fingers designed to fit within a human form factor and to move and behave more like fingers of a human hand.
2. Relevant Background
In recent years, there has been an increasing demand for robots that more closely simulate or mimic humans. For example, animatronic figures are robotic systems that are designed to duplicate characters as closely possible, and many of these characters are human or human-like characters. Robots used to provide animatronic figures may be displayed as part of rides, attractions, theater shows, retail displays, and other entertainment venues. In these settings, there is desire for the animatronic figures or robots to mimic the character, such as a character from a movie or animated film, in terms of their shape, dexterity, and ability to produce motions and forces (e.g., dynamics of a mimicked character). In addition, it may be useful for a robot to be designed to reproduce physical abilities such as walking and manipulating objects such as with fingers of a robotic hand. Many characters are made to have human characteristics or features such as hands, fingers, and the like, even when they are not a human or human-like, e.g., ants, birds, monsters, and so on with human-like hands and fingers.
Increasingly, robot designers and manufacturers are being requested to design robotic systems with human-like or anthropomorphized features and capabilities to be used in non-entertainment applications. These uses may include a robot designed for patient care in a hospital or physical therapy setting, home care for a patient, or a robot for performing household tasks. In these applications, robotic systems are expected to interact with humans in a useful manner but also in an appealing manner. Robots are generally found more appealing when they look and behave in a manner familiar to humans, and it has generally been accepted that an effective human-robot interaction is provided by a human-like robotic system or a robot with human characteristics or features such as hands and fingers.
In entertainment and other applications, a challenging and important aspect is the design of the hands of the robot. For example, the hands of a robotic character, even if the character does not have human hands, are typically designed in an attempt to mimic the form, dexterity, dynamics, and functionality of human hands. Unfortunately, none of the existing robotic hand designs have successfully met all the design challenges in presenting a robotic human hand. There are numerous end-effector designs in existence, but these are generally variations of simplistic two-fingered grippers or jaws with a single degree-of-freedom that are used to grasp or clamp objects.
Several robotic “hands” have been produced, but some of these designs only bear a greater resemblance to human hands than the two-clawed gripper but typically are lacking in terms of dexterity and form. For example, a human finger has four degrees-of-freedom (DOF) (although only 3 DOF are typically controlled independently). However, robotic hands typically have much fewer DOF with some hands only providing one DOF per band, which significantly limits their dexterity and motion capability. Some will provide one DOF per finger such that each finger can be articulated independently. However, the finger motion may be a simplistic motion such as curling upon itself with no side-to-side motion of each finger or independent movement of parts or digits of the fingers as found in a human hand.
Existing robot hands that provide increased numbers of DOF often are very complex or fail to match a human form factor. For example, one existing hand design provides 24 DOF total for the hand with relatively good finger form factor compliance, but this hand design requires the number of cables (or “tendons”) and actuators to be up to twice the number of DOF or forty-eight in this case. This results in a large form factor at the wrist and forearm that is less human in appearance. An additional problem with this hand design is that the cables or tendons used to actuate the finger movements run over fixed, un-lubricated metal or plastic runners creating significant friction and wear issues.
Another hand provides two digits for each “finger” and utilizes a pulley and actuator mechanism that does not lend itself to being packaged with human form factor (e.g., thin elongated fingers, a relatively small wrist, and thin palm). Particularly, in this hand design, an “n+1” arrangement is used for the drive cables or tendons, which reduces the number of cables required, but the pulley arrangement is such that the cables each wrap about their supporting pulleys by more than 360 degrees, which requires that the pulleys be thick (e.g., generally twice the cable thickness) making it difficult to place in a finger form factor packaging. Also, the cables create additional friction and wear as they cross over one another and rub upon each other during operation of the hand. Further, this robot hand requires four motor drives per finger, which increases costs, complexity, form factor, and maintenance.
Yet other robotic hands may be designed to use a thicker cable and actuate the fingers with a push/pull arrangement. Motors are proximally mounted to the wrist that is used to support the hand. To transmit power through the wrist, flexible drive shafts are used, with rotary motion as opposed to linear motion being transmitted through the wrist. This rotary motion is converted to linear motion by means of lead screws mounted in the palm of the hand. This provides the advantage of passing a number of drive shafts equal to the number of DOF of the hand (e.g., twelve in one example of this design). However, one disadvantage of the rotary drive hand is that twelve lead screws must be packaged within the palm of the hand, resulting in a large (i.e., greater than human-sized) palm. Also, the use of a thick cable in a push/pull arrangement to actuate the finger DOF limits the amount of force that may be applied in the “push” direction, which may limit the uses of this robotic hand design.
Hence, there remains a need for hand design for a robot or robotic system that meets the challenges associated with a human form factor while achieving the functionality expected of a human hand. It is preferable that such a hand design would include fingers with a similar number of digits as found in a human hand and with dexterity and movement that is more human like (e.g., fingers that move with a similar number of DOF). It is also preferable that the robot hand design includes a relatively small number of components and addresses wear and maintenance issues associated with use of actuating cables (or tendons).